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Discussion
The Abstractor Notes currently do not explain the histologic classification of follicular lymphoma [FL]. Frequently, FL grade 1 and 2 are not being separated and are described as “low grade” or “grade 1-2” in the pathology final diagnosis. The correct histology code would be 9691/3 [FL, grade 2] for these cases. Apparently, per the 2008 WHO Classification, grade 1 and grade 2 are being grouped together as grade 1-2 due to the minimal difference in patient outcome. If these histologies are grouped together, will histology code 9695/3 [FL, grade 1] ever be used? Should the Heme Database explain the classifications of follicular lymphoma grade 1, 2, and 3?

Answer
When the latest WHO classification for heme neoplasms was written in 2008, there was a lot of controversy about whether or not the FL grading system was useful or not. A number of papers have been written stating that grades 1 and 2 do not have a statistically different survival or transformation rate. Given that the controversy had not been settled by those in the clinical world, the WHO recommended analyzing grades 1 and 2 together. They did not, however, remove either grade 1 or 2 from their classification. When the WHO intend to change their classification (have both grades classified under one histology number), they omit one code from their book (make it obsolete) and change the definition for the other code. The 2008 WHO book did not make either ICD-O-3 code obsolete. Therefore, we continue to collect the cases as designated by the pathologist. If the controversy is settled before the next WHO classification, you may see changes in the codes.

Additionally, since the 2008 WHO book was written, there have been some clinical papers challenging the designation of grade 3. They contend that grade 3 can be mistaken for low-grade.

The grades for follicular lymphoma are based on the number of centroblasts per high powered field (HPF). The number of centroblasts for grade 1 is 0-5; for grade 2 is 6-15, for grade 3a and 3b is >15 centroblasts. 3a has centrocytes and 3b has no centrocytes.